Not long ago, a report surfaced on a Friday that a roadside bomb in Iraq had been hidden inside a dead dog. By the following Monday, the general who oversees the Army's training centers recalled, Army trainers back in the United States had copied the trick.

"It's a truly dynamic curriculum" at the training centers, changing as new tactics emerge in the fighting in Iraq, Lt. Gen. William S. Wallace said in an interview.

Fifteen months of combat in Iraq are leaving an imprint on the U.S. military. All the services are changing, but the Army especially is undergoing radical change as a result of the unexpectedly difficult occupation, in which it has suffered nearly 6,000 casualties.

The strain on Army troops, families and equipment has been extensively reported and is likely to intensify as some units head back to Iraq for a second tour. "The war in Iraq is wrecking the Army and the Marine Corps," retired Navy Capt. John Byron asserts in the July issue of Proceedings, the professional journal of Navy officers. "Troop rotations are in shambles and the all-volunteer force is starting to crumble as we extend combat tours and struggle to get enough boots on the ground."

The latest indication of the psychic toll was a recent study by the Walter Reed Army Institute of Research that found that about 16 percent of soldiers who have served in Iraq are showing signs of combat trauma.

Overall, "this kind of stress causes change -- some of it good, some of it not so good," said Sen. Jack Reed (D-R.I.), a former Army officer who serves on the Senate Armed Services Committee.

Indeed, other, less visible changes also are occurring -- and some of them are for the better. A generation of younger Army officers has been seasoned by a year of combat in a harsh and unpredictable environment, for example. And as the Army seeks to adjust to waging a counterinsurgency campaign 7,000 miles away, innovation in how it trains new recruits and structures forces for deployment is now rippling through the service.

"Iraq is accelerating the pace of change in the military -- the Army particularly," said retired Army Lt. Col. James Jay Carafano, a defense analyst at the Heritage Foundation. "It is forcing them to look at a lot of things they had pushed off because they were hard to do."

In the other services, the changes seem to be mainly financial. At the Navy's big East Coast base in Norfolk, fewer tugboats will be on call this summer to help steer warships to their berths, a result of a decision to tighten base budgets to free up $300 million to help pay for Navy and Marine operations in Iraq. The sea service also is deferring purchases of some spare parts until the new federal fiscal year begins, in October.

"There may be some degradation of readiness as a result," said Vice Adm. Cutler Dawson, deputy chief of naval operations for resources. He also said he thought the effect would be short-term.

At the Air Force, trims are being made in the budgets for travel, transfers, and some purchases of parts and supplies. "We're attempting to minimize any of the readiness impacts," said Maj. Gen. Steve Lorenz, the Air Force's budget director. "We won't know until the end of the year how it all shakes out."

There is no question that the Army personnel system is stressed. "I think the Army is in terrible shape," said retired Army Lt. Gen. Jay M. Garner, who served last year as the Bush administration's first administrator in postwar Iraq. "I think people are worn out, equipment is run down and we've overstressed the reserves. We're drastically short [of] infantry and MPs because the Army is too small."

Other experts worry about the hidden costs of using up equipment in the extreme heat and abrasive dust of Iraq. Helicopters, armored vehicles and Humvees will have shorter service lives than the Army planned. "Equipment's taking a beating. Aircraft and high-cost tank engines are accumulating lots of hours," said retired Army Lt. Gen. Leonard Holder.

In the Army, the biggest long-term changes may be in how it trains -- if the lessons learned in counterinsurgency stick. After the Vietnam War, noted retired Army Lt. Col. Andrew F. Krepinevich Jr., who wrote a book on the Army and Vietnam, "we got out of the counterinsurgency business."